Decoys are often used in combat to confuse enemy aircrafts and ships and spoil the aim of their weapons. To increase decoy useful life and also to separate or offset the decoy from the craft, cable-towed decoys are often preferred.
To operate at high altitudes/low densities increases in drag parameter C.sub.D S or equivalent flat plate area "S" are required to damp cable oscillations and avoid cable instabilities. Cable tension increases with speed and dynamic pressure, then operations are limited by cable strength at high dynamic pressures. Further, violent evasive maneuvers represent very large additional excursions from steady state cable tension values, the so-called "whip" effect, resulting in additional restrictions on the decoy operational envelope.
Two conditions must be improved: the ability to get large decoy forces, mostly from large equivalent flat plate areas, even in maneuvers at high altitudes and low speeds, and also the ability to modulate decoy forces to avoid breaking the cable at high dynamic pressures.
Parachutes can generate very large drag forces but force modulation is a big problem and they also interfere with critical decoy requirements in the rear quadrant. Negative lift forces could also be considered to increase the pull at the end of the cable. But, lift forces are very sensitive to angle of attack, controlled by the pitching moments generated by cable forces relative to the center of gravity. Substantial variations are expected since the cable angle at the decoy is very sensitive to conditions and can easily vary 45.degree. or more. Difficult packaging also a major problem, and at supersonic speeds, their effectiveness decreases with increasing mach number.
Thus, we are looking for impact or streamwise forces, generated by solid aerodynamic surfaces which can be controlled and yet will not interfere with radiation or signals from the base of the decoy.
Fins matching the body contour can be nearly as long as the body, thus featuring high span to chord ratios giving very large coefficients approaching two-dimensional optimum values, and also a vary large total area when a plurality of fins represents a good percentage of the body surface area. Packaging problems become manageable. Force modulation also becomes relatively simple when these fins are always in a swept-back configuration. Increasing fin forces will increase sweepback angles which tend to decrease fin and decoy drag levels, minimizing changes in cable tension.